ELECTRONIC AND BONDING PROPERTIES OF MIXED-LIGAND PYRIDINE-2,6-DICARBOXYLATE COPPER(II) COMPLEXES - MOLECULAR-STRUCTURES OF IMETHYLAMINOPYRIDINE)(PYRIDINE-2,6-DICARBOXYLATO)] AND LIMIDAZOLE)(PYRIDINE-2,6-DICARBOXYLATO)(0.5H(2)O)]

Mixed-ligand pyridine-2,6-dicarboxylatocopper(II) complexes. [Cu(dipic )(L)] [dipic = pyridine-2,6-dicarboxylate, L = imidazole, N-methylimid azole (nmim), 4-methylimidazole, pyridine, 4-methylpyridine, 4-aminopy ridine, 4-dimethylamino-pyridine(4dmapy) and NH3 . H2O], have been syn thesized and characterized by elemental analyses, and UV-vis, IR and E PR spectroscopic measurements. Molecular structures of [Cu(dipic)(4dma py)] (1) and [Cu(dipic)(nmim)(H2O)(0.5)] (2) have been determined by X -ray diffraction methods. Complex 1 is square planar and 2 comprises b oth square pyramidal [Cu(dipic)(nmim)(H2O)] and square planar [Cu(dipi c)(nmim)] units. The equatorial heterocyclic unidentate ligands are ne arly co-planar with the CuN2O2 coordination plane : 1.3 degrees for 1, 6.8 degrees and 13.9 degrees for the square plane and square pyramid, respectively, of 2. The structures of other heterocyclic complexes ar e suggested to be square planar based on their spectroscopic data. The sequence of d orbitals was assigned as d(x)2(-y)2 >> d(xz) > d(xy) > d(yz) > d(z)2 for the square planar complexes and d(x)2(-y)2 >> d(z)2 > d(xz) > d(yz) for the square pyramidal NH3 complex. The significant rise in energy of the d(xz) orbitals suggests that the central pyridin e nucleus of the dipicolinate ligand and the heterocyclic unidentate l igands are pi-donors. This is attributable to ionic bonding effects. C opyright (C) 1996 Elsevier Science Ltd.